In the open ocean, the prevailing color is a deep greenish blue; other shades observed in the different seas seem to be owing to local causes. In shoal places the water takes a lighter hue. The luminous appearance of the sea by night is a magnificent phenomenon, that has not yet been entirely explained. The great divisions of the sea are inhabited by their peculiar fish, and frequented by peculiar species of birds. The level of the sea is, generally speaking, every where the same; though exceptions to this rule are sometimes found in land-locked bays and gulfs, where the waters become accumulated and stand higher than in the open ocean. CHAPTER XIII.――SOIL. EVERY variety of soil is found within the territory of the United States, and an accurate general estimate is not of course to be formed. We will first describe that portion of the country known as the Atlantic Slope. Next to the ocean are salt meadows or marshes, but little elevated above the water, towards which, their surface has a very slight inclination. They are covered with a peculiar reddish grass, from six to twelve inches in height, growing very thick, and forming with its roots a compact turf or sward, which is only cut with a sharp instrument and by considerable force. These meadows are overflowed by the salt water a few inches deep, several times every spring, and to this their peculiar character is attributed; for when the water is kept from them by dikes, the upland grasses take root, the turf loses its tenacity and crumbles, and in a few years their appearance is entirely changed. A slope of about six feet in two or three rods lies between these meadows and low water mark; this is covered with a coarse tall grass called sedge, which requires the returns of the daily tides to bring it to maturity.